Method for improving the bonding of nylon filaments by the use of a hydrogen halide gas

ABSTRACT

A process for improving the bonding efficiency of nylon fibers for the formation of a high-strength spunbonded fabric including preparing the fibers for bonding by increasing the moisture regain of the nylon fibers which comprise a mat to at least 2% based on the weight of the fiber, subjecting the mat to a gaseous atmosphere containing less than 2% by volume of a hydrogen halide gas and greater than about 0.5% by volume of water vapor to increase the moisture regain of the nylon to at least 3% based on weight with said fibers absorbing at least 2% of the hydrogen halide gas based on weight and completing the bonding of the fibers by pressing the fibers together while the fibers contain the mentioned water and hydrogen halide gas and by removing the hydrogen halide gas from the fibers.

United States Patent Rhodes Dec, 10, 1974 METHOD FOR IMPROVING THE BONDING OF NYLON FILAMENTS BY THE USE OF A HYDROGEN HALIDE GAS [75] Inventor: Jerome H. Rhodes, Raleigh, NC.

[73] Assignee: Monsanto Company, St. Louis, Mo.

[22] Filed: Dec. 29, 1972 [21] Appl. No.: 319,132

[52] US. Cl 156/181, 156/308, 161/150,

161/227, 161/411, 264/83 [51] Int. Cl. D04h 3/12, C09j 5/02 [58] Field of Search 156/307, 308, 181; 161/150, 227, 411; 264/83 [56] References Cited UNITED STATES PATENTS 3,516,900 6/1970 Mallonee et a1. 161/150 Primary ExaminerCharles E. Van Horn Assistant ExaminerRobert A. Dawson [57] ABSTRACT A process for improving the bonding efficiency of nylon fibers for the formation of a high-strength spunbonded fabric including preparing the fibers for bonding by increasing the moisture regain of the nylon fi-,

bers which comprise a mat to at least 2% based on the weight of the fiber, subjecting the mat to a gaseous atmosphere containing less than 2% by volume of a hydrogen halide gas and greater than about 0.5% by volume of water vapor to increase the moisture regain of the nylon toat least 3% based on weight with said fibers absorbing at least 2% of the hydrogen halide gas based on weight and completing the bonding of the fibers by pressing the fibers together while the fibers contain the mentioned water and hydrogen halide gas and by removing the hydrogen halide gas from the fi- 3,542,615 11/1970 Dobo et a1. 156/181 bers I 3,555,806 1/1971 Knudsen et al. 57/153 3,676,244 7/1972 Kim 156/181 4 Claims, 1 Drawing Figure WEB PRECONDITIONING BONDlNG GAS GAS FAB'mC FORMATION CHAMBER g m'ggg Q Q TAKE- UP I METHOD FOR IMPROVING THE BONDING OF NYLON FILAMENTS BY THE USE OF A HYDROGEN I-IALIDE GAS BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a process for transforming an unbonded fibrous mat of nylon fibers into a high strength bonded non-woven web and, more particularly, an improved process for rendering nylon fibers bondable to each other at their touching cross-over points.

2. Description of the Prior Art Bonding nylon fibers by means of a hydrogen halide gas and, more particularly, hydrogen chloride gas is a developing art. The advantages ofbonding nylon fibers together by this technique which is referred to as autogenous bonding are that foreign substances are not interjected into the nylon polymer which would change the characteristics of a homogenous nylon non-woven fabric and that polymer migration to the bonded filament intersections which is a result of the dissolution and re-deposition of polymer is minimized or eliminated. U.S. Pat. No. 3,516,900 to Mallonee et al. first disclose autogenous bonding by means of an activating gas such as hydrogen chloride gas. Mallonee et al subjected nylon fibers to a hydrogen chloride gas, allowed the fibers to absorb quantities of the hydrogen chloride gas, placed the fibers in intimate contact with each other, and removed or desorbed the hydrogen chloride gas from the fibers by means of either heat or a wash water bath. The result was a bond formed at the touching cross-over of the various fibers.

In U.S. Pat. No. 3,542,615 to Dobo et al., it was contemplated that a self-bonded, non-woven fabric could be produced from a polymer melt in a single continuous operation. Continuous nylon filaments were spun from a polymer melt, pneumatically attenuated and deposited onto a moving surface or conveyor belt in the form of an unbonded mat. The continuous filaments comprising the mat were arranged without apparent order. The mat was advanced through a chamber filled with an activating gas and was allowed to remain therein a time sufficient topermit surface absorption of the gas into the filaments. The'fibrous mat containing the absorbed gas was calendered to improve contact between filaments. Thereafter the gas was desorbed or neutralized by exposing the mat to a wash water bath or to a heated environment whereby interfilament bonding was completed.

In U.S. Pat. No. 3,676,244 to Kim, it was recognized that the addition of moisture or moisture regain of the nylon filaments prior to being introduced into the gas box greatly improved bonding efficiency. It was found that the tensile strength of the resulting web was greatly increased by elevating the water content or moisture regain of the filaments to a range of from 3% to 6% based on the weight of the nylon filaments prior to the contact of the filaments with the activating gas. A mat of unbonded nylon filaments was passed through a humidifying unit where the nylon filaments regained at least 3% moisture based on the weight of the nylon.

SUMMARY OF THE INVENTION In its broadest aspects, the present invention contemplates the formation of a non-woven web which is comprised of nylon filaments, the filaments being autoge nously bonded together at a substantial number of touching filament cross-over points. Specifically, the invention is the special handling of the nylon filaments prior to their entrance into the gas box, during the residing time in the gas box and subsequent to the gas box which includes the pressing of the fibers together while the fibers are in said conditioned state. The nylon fibers which comprise the unbonded mat are prepared for bonding by increasing the moisture regain thereofto at least 2% based on the weight of the fiber. The mat is then subjected to a gaseous atmosphere containing less than 2% by volume of a hydrogen halide gas and greater than about 0.5% by volume of water vapor to increase the moisture regain of the nylon to at least 3% based on the weight of the fibers and to allow the nylon fibers to absorb at least 2% hydrogen halide gas based on the weight of the fibers. Bonding of the fibrous mat to form the non-woven web is completed by pressing the fibers together while the fibers contain the mentioned water and hydrogen halide gas and by removing the hydrogen halide gas from the fibers subsequent to pressing preferably by means of a water wash bath. Moisture regain" is the amount of water on a weight basis present in the nylon fiber as compared to the weight of the nylon fiber in the dry state.

DESCRIPTION OF THE DRAWINGS This invention can be more thoroughly understood by referring to the drawing wherein:

The FIGURE is a block diagram showing the various process steps throughwhich the nylon is passed.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT standard abrasive element is an S32 wheel. The disc after having received fabric is rotated at a speed of 72 rpm. Fabric failure is determinedwhen six filaments have been raised at least one-eighth of an inch above the surface of the fabric. For the purposes of determining adequate bonding, the fabric must pass at least five revolutions beneath the abrading element without having six filaments raised to at least one-eighth of an inch above the surface of the fabric. Hereinafter, this test will be referred to as the Taber abrasion test.

The mat of unbonded nylon fibers may be formed by means ofa variety of methods. The fibers may be either staple or continuous filament. However, for the purposes of this invention, the unbonded mat of fibers shall be formed by the method taught in U.S. Pat. No. 3,542,615 to Dobo et al, and therefore, the filaments will be continuous. Basically, the continuous nylon filaments are spun from a nylon polymer melt, after which the filaments are attenuated and forwarded to a moving foraminous belt for collection. Themat of continuous unbonded nylon filaments are forwarded to a preconditioning chamber which is maintained. at a controlled humidity level in order to provide a moisture regain of at least 2%.

When converting fibrous mats into bonded webs under commercial process conditions, the dwell time at each process step is less than 60 seconds. It has been found that nylon filaments do not readily absorb a hydrogen halide gas such as, for example, hydrogen chloride gas to the extent necessary to provide adequate bonding which is approximately 2% and above. Also, the nylon filaments must regain at least 3% moisture based on the weight of the fibers. Although the bonding and moisture chamber contain quantities of water vapor, the dwell time therein does not permit the moisture regain of at least 3% nor the subsequent absorption of the gas to at least 2% based on the weight of the fiber without the filaments having regained at least 2% moisture prior to entrance into the bonding gas and moisture chamber.

Conditions in the bonding gas and moisture chamber are also critical. when the process is run at the contemplated commercial speeds, the swell time in the bonding gas and moisture chamber is no greater than 40 seconds. Therefore, moisture regain and absorption of the hydrogen halide gas into the nylon fibers must occur rapidly. Thus, the content of the gaseous atmosphere within the mentioned chamber becomes critical. The temperature must range between 50 and 120F. Below 50F. sufficient moisture is not available within the chamber to allow the required moisture regain to take place and, at above lOF., both the moisture and the absorbed hydrogen halide gas have a tendency to be volatilized from the filaments. The balance between the volume of the hydrogen halide gas and the volume of water vapor present in the gaseous atmosphere is also critical. It would seem logical where it is desirable to increase the hydrogen halide gas content to a predetermined level to increase the volume of gas within the gaseous atmosphere. However, such is not possible since, at greater concentrations, the hydrogen halide gas depresses the dew point of the gaseous atmosphere to levels where moisture is not available within the gaseous atmosphere to raise the moisture regain to the required 3% based on the weight of the fibers. It has been found that at least 0.5% by volume of water vapor should be present within the gaseous atmosphere in order to provide a regain of at least 3% based on the weight of the fibers. However, water must not be available within the gaseous atmosphere to the extent that the dew point of the same is reached. If the dew point is reached, condensation will occur within the bonding gas and moisture chamber in the form of hydrochloric acid. Any contact by the nylon fibers with the hydrochloric acid results in the destruction of the nylon since hydrochloric acid is a known solvent for nylon.

Upon exiting the bonding gas and moisture chamber, it is critical that the nylon fibers maintain the abovementioned percentages of hydrogen halide gas and moisture for, if the moisture is allowed to evaporate from the fibers to the degree where the fibers contain less than 3% moisture regain based on the weight of the fibers, the fibers lose their surface tackiness and will not readily adhere to each other when pressed together. Therefore, conditions are to be maintained in the area between the bonding gas and moisture chamber and the press rolls such that moisture will not be lost from the fibers. Pressing is generally accomplished by means of calender-type press rolls which may or may not be embossed. Once the mat of fibers proceeds through the press rolls, the filaments are in intimate contact and bonding is completed by removing the hydrogen halide gas therefrom. While the hydrogen halide gas may be removed or desorbed from the bonded web by heat means, it is preferred to-pass the web through a water wash bath. Once the hydrogen halide gas is removed from the filaments, bonding is complete. The bonded web is then dried and packaged by any suitable take-up means.

EXAMPLE I A mat of continuous nylon 66 filaments was prepared by the standard spunbonded process which includes spinning nylon filaments, attenuating the filaments and forwarding thefilaments to a moving foraminous belt for collection. The unbonded mat weighed approximately 1.0 oz. per square yard. The mat, in its unbonded state, was subjected to the preconditioning chamber. The mat had a moisture content entering the preconditioning chamber of 1.5% based on the weight of the mat. The temperature of the preconditioning chamber was F. and the relative humidity was 60%. The mat was exposed to the atmospheric conditions in the preconditioning chamber for approximately 40 seconds. Upon leaving the preconditioning chamber the moisture regain of the mat was 2.2%.

The mat was then subjected to the bonding gas and moisture chamber. The chamber contained 0.9% by volume of the hydrogen chloride gas and 1.3% by volume of water vapor. The temperature within the chamber was 92F. which was approximately 16 above the saturation or dew point for that particular atmospheric condition. The mat was exposed to the conditions within the bonding gas and moisture chamber for approximately 12 seconds. Upon leaving the bonding gas and moisture chamber, the mat picked up 4.0% by weight of the hydrogen chloride gas and had a total moisture regain of 4.8% by weight.

The fibrous mat was then pressed by being passed through cooperating calender rolls, the rolls exerting a net pressure of pounds per linear inch. Interfilament bonding was completed by passing the mat through a water wash bath which removes or desorbs substantially all of the hydrogen chloride gas from the filaments. The resulting bonded web was then dried.

A sample of this web was then tested by means of the Taber abrasion test method. The web passed seven cycles before failure.

This Example showed that adequate bonding can be achieved with relatively low moisture and HCl concentrations within the mat and with medium dwell times in the bonding gas and moisture chamber which was 12 seconds.

EXAMPLE 11 The basic process steps of Example I were repeated with the changes being made in the preconditioning chamber and the bonding gas and moisture chamber.

Preconditioning Chamber Moisture of Mat Entering 1.8% by weight Exposure Time 9 seconds Temperature 59F.

Relative Humidity 74F.

Moisture of Web Leaving 2.2%

Bonding Gas and Moisture Chamber Bonding Gas and Moisture Chamber Conditions Hydrogen Chloride Gas Concentration 1.0% by volume Hydrogen Chloride Gas Concentration 1.2% by volume Water Vapor Concentration 1.7% by volume w vapor concentration 0,3 7 by mhlme Temperature 8"F. Temperature 84F. Degrees Below Saturallo 2 F- 5 Degrees Below Saturation 14F. Exposure Tlme 4 Seconds Time Exposed 12 seconds T gaszd a s h fl i ig gas a Upon leaving the bonding gas and moisture chamber i l 21; a Y g F f z'g g j t0 the web contained 5.6% by weight of the hydrogen ra 0 0 y welg an a mols ure regain? chloride gas and had a moisture regain of 8.4% by by weight. When sub ected to the Taber abrasion test,

. weight. The bonded web withstood 23 cycles on the the sample only withstood four cycles before failure.

. Taber abrasion apparatus. The reason this sample failed was because at a dwell time of only four seconds the nylon filaments only EXAMPLE v picked up 1.6% by weight of the hydrogen chloride gas and, therefore, bonding was unsatisfactory. Thus, at T baslc gi Steps of H were repeated short dwell times with low moisture regain, the fila- 6 process con Hons are as 0 ments are not able to absorb an hydrogen chloride gas from the gaseous atmosphere mixture readily enough Preconditioning Chamber to allow more proper bonding.

Moisture of Web Entering 1.8% by weight Time Exposed 20 seconds Temperature 75F. EXAMPLE "I Relative Humidity 95% 25 Moisture of Web Leaving 4.9% by weight The basic process steps of Example I were repeated. The process conditions are as follows:

Preconditioning Chamber Moisture of Mat Bonding Gas and Moisture Chamber Conditions Hydrogen Chloride Concentration 0.4% by volume Time lgz g gf Water Vapor Concentration 1.8% by volume T 7505 Temperature 86F. zmmi fifi Degrees Below Saturation 2F. Moisture of Mat Leaving 4.2% Time Exposed f 8 seconds Upon leaving the bonding gas and moisture chamber, I the mat had a moisture regain of 6.0% by weight and Bmdmg Gas and Mms'ure Chamber picked up 4.0% by weight of the hydrogen chloride gas. Hydrogen Chloride Gas Concentration 0.3% by volume 40 The resulting bonded web had a life of eight cycles on Water Vapor Concentration 1.5% by volume Temperature 82F the Taber abrasion apparatus. I Degrees Below Saturation This Example shows that at shorter dwell times, ade- Tlme P 12 Seconds uate bondin can be achieved if conditions in the q 2 bonding gas and moisture chamber are maintained se to saturation The gassed mat had a hydrogen chloride gas concen- Clo tration of 5.6% by weight and had a moisture regain of EXAMPLE V1 8.1? b wei ht. The resultin sam le was su'b'ected to x 0 y g g p J The basic process steps of this Example are identical the Taber abrasion apparatus and had a life of 19 cycles t th tf th E l I Th which indicates a very highly bonded web. It will be XamP e e Pmcess noted that at high moisture regain levels and medium are as 0 dwell times, the hydrogen chloride gas conditions are less Crmcal Preconditioning Chamber Moisture of Mat Entering 1.6% EXAMPLE IV Time Exposed seconds Temperature 75F. Rel t' Hum'dit 807 The basic process steps of Example I were repeated. 231; of 1 {caving 4%!3y weight The process conditions are as follows:

Preconditioning Chamber Bonding Gas and Moisture Chamber Conditions Moisture of Mat Entering 1.5% by weight Hydrogen Chloride Gas Concentration 5.5% by volume Time Exposed gg econds lrllater Vapor Concentration 0.3% by volume emperature emperature 74F. Relative Humidity 5 Degrees Below Saturation 15F. Moisture of Mat Leaving 4.2% Time Exposed 24 seconds Upon leaving the bonding gas and moisture chamber, the mat contained 2% by weight of the hydrogen chloride gas and had a moisture regain of 2.5% by weight. The resulting bonded web had a life of only three cycles on the Taber abrasion apparatus. Therefore, bonding was inadequate and the sample failed. This Example shows the importance of water vapor in the bonding gas and moisture chamber. It is recognized that the moisture level of the fibers leaving preconditioning was adequate. It is also recognized that the dwell time in the bonding gas and moisture chamber was more than adequate and that the concentrations of the hydrogen chloride gas within the box was high. Even with a high level of moisture contained by the mat upon entering the bonding gas and moisture chamber, the percent moisture regained upon leaving the bonding gas and moisture chamber had been reduced to 2.5% by weight. The reason for this reduction is that the water vapor within the bonding gas and moisture chamber was only 0.3% by volume and, in fact, 1.5% by weight of moisture evaporated from the web. Thus, hydrogen chloride gas absorption by the fibers is a direct result of the amount of total moisture regained by the fibers.

I claim:

1. A process for transforming an unbonded fibrous mat of nylon fibers into a high-strength bonded nonwoven web comprising the steps of:

A. preparing the fibers for bonding by 1. increasing the moisture regain of said nylon fibers to at least 2% based on the weight of said nylon fibers;

2. subjecting said mat to a gaseous atmosphere having a temperature of from 50 to 120F. and containing less than about 2% by volume of a hydrogen halide gas and greater than about 0.5% by volume of water vapor, but lower than the dew point of said water vapor--hydrogen halide gas mixture at any given gaseous atmosphere temperature, said nylon fibers increasing said moisture regain to at least 3% based on weight of said fibers and absorbing at least 2% of said hydrogen halide gas based on the weight of said fibers; and

B. completing the bonding of said fibers by l. pressing said fibers together while said fibers contain said water and hydrogen halide gas; and 2. removing said hydrogen halide gas from said fibers. 2. The process of claim 1 wherein said hydrogen halide gas is hydrogen chloride gas.

3. The process of claim 1 wherein said nylon fibers are continuous nylon filaments.

4. The process of claim 1 wherein hydrogen halide gas is removed by means of a water wash bath. 

1. PRESSING SAID FIBERS TOGETHER WHILE SAID FIBERS CONTAIN SAID WATER AND HYDROGEN HALIDE GAS; AND
 1. A PROCESS FOR TRANSFORMING AN UNBONDED FIBROUS MAT OF NYLON FIBERS IBINTO A HIGH-STRENGTH BONDED NON-WOVEN WEB COMPRISING THE STEPS OF: A. PREPARING THE FIBERS FOR BONDING BY A. INCREASING THE MOISTURE REGAIN OF SAID NYLON FIBERS TO AT LEAST 2% BASED ON THE WEIGHT OF SAID NYLON FIBERS;
 2. SUBJECTING SAID MAT TO A GASEOUS ATMOSPHERE HAVING A TEMPERATURE OF FROM 50* TO 120*F. AND CONTAINING LESS THAN ABOUT 2% BY VOLUME OF A HYDROGEN HALIDE GAS AND GREATER THAN ABOUT 0.5% BY VOLUME OF WATER VAPOR, BUT LOWER THAN THE DEW POINT OF SAID WATER VAPOR-HYDROGEN HALIDE GAS MIXTURE AT ANY GIVEN GASEOUS ATMOSPHERE TEMPERATURE, SAID NYLON FIBERS INCREASING SAID MOISTURE REGAIN TO AT LEAST 3% BASED ON WEIGHT OF SAID FIBERS AND ABSORBING AT LEAST 2% OF SAID HYDROGEN HALIDE GAS BASED ON THE WEIGHT OF SAID FIBERS; AND B. COMPLETING THE BONDING OF SAID FIBERS BY
 2. REMOVING SAID HYDROGEN HALIDE GAS FROM SAID FIBERS.
 2. subjecting said mat to a gaseous atmosphere having a temperature of from 50* to 120*F. and containing less than about 2% by volume of a hydrogen halide gas and greater than about 0.5% by volume of water vapor, but lower than the dew point of said water vapor--hydrogen halide gas mixture at any given gaseous atmosphere temperature, said nylon fibers increasing said moisture regain to at least 3% based on weight of said fibers and absorbing at least 2% of said hydrogen halide gas based on the weight of said fibers; and B. completing the bonding of said fibers by
 2. removing said hydrogen halide gas from said fibers.
 2. The process of claim 1 wherein said hydrogen halide gas is hydrogen chloride gas.
 3. The process of claim 1 wherein said nylon fibers are continuous nylon filaments.
 4. The process of claim 1 wherein hydrogen halide gas is removed by means of a water wash bath. 